[LLVMdev] How to locate the start if an address mode in an X86 MachineInstr?

[Craig Topper]

I think getMemoryOperandNo in X86BaseInfo.h is what you want. That's what
the MC code emitter uses to encode the memory operand.

On Thu, Sep 20, 2012 at 1:41 PM, Gurd, Preston <preston.gurd at intel.com>wrote:

> My team interested in doing some post-RA optimizations on X86
> instructions, which would require identifying memory reference instructions.
>
> In the X86 back end instructions, memory addresses consist of a set of
> five operands. The offset to the start of the five operands depends on the
> format of the instruction. For instance, the instructions ADC32rm, ADD32rm,
> AND32rm, ANDN32rm, CMOVA32rm, CMOVAE32rm, CMOVB32rm, et al. all have a 32
> bit memory address set starting at operand 2.
>
> There does not seem to be any way to obtain the offset to the start of a
> memory reference in an X86 MachineInstr.
>
> Tablegen code is able to determine the offset when it generates the
> X86GenAsmWriter.inc file at build time. That code obtains the offset
> indirectly from the OpInfo table entry for an opcodes, which involves
> extracting a bit field from the OpInfo Entry, then using the extracted code
> in a switch statement to print out the operands for a particular class of
> instruction.
>
> Would you know if there is a way, given a MachineInstr, to obtain the
> address offset?
>
> Or, if not, could you sketch out a way to do that?
>
> Thanks,
>
> Preston
>
> --
> Preston Gurd <preston.gurd at intel.com>
>   Intel Waterloo
>   SSG/DPD/ECDL/DMP
>
>
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-- 
~Craig
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